1. Field of Invention
This invention relates to an exposure device that illuminates a mask with illumination light that is irradiated from an illumination optical system and exposes a pattern formed in a mask onto a substrate, and in particular, to a preferred exposure device in which at least part of an illumination optical system is disposed within a case.
2. Description of Related Art
FIG. 5 shows an example of one type of exposure device. The exposure device 1 shown in this figure provides an exposure device main body 3 and a temperature adjusting device 4 within a chamber 2. The exposure device main body 3 mainly includes an illumination optical system 5, a reticle stage 6 that holds a reticle (mask) R, a projection optical system 7, and a substrate stage 8 that holds a substrate P and is housed in a temperature adjusting chamber 11, which is located within the chamber 2.
The illumination optical system 5 shown in FIG. 6 selects a necessary wave length from a light beam generated from a light source 9 and illuminates the reticle R that is held on the reticle stage 6 with exposure light in which illumination is evenly distributed (made uniform).
The projection optical system 7 projects an image of a pattern PA of the reticle R illuminated with the exposure light onto the substrate P that is held on the substrate stage 8. A reticle alignment detection system 10 is disposed between the illumination optical system 5 and the reticle stage 6. The reticle alignment detection system 10 detects a reference mark FM disposed on the substrate stage 8 through the projection optical system 7 and detects an alignment reticle mark RM formed on the reticle R. By calculating the shift between the reticle R and the substrate stage 8 based upon the detection results, positioning between the reticle R and the substrate stage 8 is performed.
The temperature adjusting device 4 adjusts the temperature of air within the temperature adjusting chamber 11 which is taken in from a return duct 12 and air that is taken in from an external air intake 13, to a predetermined temperature, and sends temperature-adjusted air through jets (inlets) 15 of a partition wall 14 into the temperature adjusting chamber 11. A filter (not depicted) to remove dust in the air is disposed over the jets 15. The air in the temperature adjusting chamber 11 is temperature-adjusted by the temperature adjusting device 4, and thereby maintains an environment having a constant temperature and cleanliness in which dust is removed, by the filter.
Recently, there has been observed a phenomenon in which particles become attached to a surface of a glass component, for example, an optical element within the illumination optical system 5. This drastically decreases the illumination when the pattern PA of the reticle R is projected onto the substrate P. This phenomenon occurs because, for example, when an ArF excimer laser is used as a light source 9, its emission spectrum overlaps an oxygen absorption spectrum area, causing ammonium sulfate to be generated as the light usage efficiency due to oxygen absorption decreases. Chemical components included in the air within the temperature adjusting chamber 11 undergo a photochemical reaction by ultraviolet light (particularly light and the like of the wavelength shorter than the i beam) generated from the light source 9 within the illumination optical system 5. The product of this photochemical reaction (the above-referenced particles) become attached to the glass components.
As a strategy to combat this problem, a method called an N.sub.2 purge is used in which the illumination optical system 5 is stored within a case, a degree of sealing of which is made to be high within the illumination optical system 5 except in the vicinity of the light source 9. The case is filled with a gas that is inert for the photochemical reaction and has a small amount of light absorption, such as N.sub.2 gas. This makes it difficult for the photochemical reaction to occur. By using this method, an impurity such as ammonium sulfate attached to glass components within the illumination optical system 5 was decreased, but an operation interval to remove such an impurity was made to be significantly long.
However, a conventional exposure device described above has the following problems. The illumination optical system 5 generates a large amount of heat because it has an optical path including the light source 9. Because of this, in a conventional illumination optical system 5, as shown in FIG. 6, an air intake 16 and a heat emission duct 17 are provided. Heat generated in the air from the illumination optical system 5 is emitted from the system 5 by taking in air through air intake 16 and emitting heat from heat emission duct 17. Thus, the surface temperature of the optical elements that form the illumination optical system 5 did not become too high.
However, because other optical elements excluding the light source 9 were separated by an N.sub.2 purge in a state in which the degree of sealing was made to be high, heat emission from the sealed part was inhibited, the heat was confined in the N.sub.2 purge area, and the surface temperature of this part became high.
When the surface temperature of the illumination optical system 5 becomes high, the temperature of the vicinity of the illumination optical system 5 increases, and air fluctuation is generated by this heat. Because of this air fluctuation, in the reticle alignment detection system 10, which is located near the illumination optical system 5, there was a problem in which accuracy became poor in the case of detecting the reference mark FM and the reticle mark RM.